The present invention relates to high voltage motor controllers and the like, and more particularly to an improved drawout carriage assembly for bearing a contactor.
Starting, stopping and current flow monitoring of large electric motors is conventionally carried out by apparatus termed motor control centers, or motor controllers. Such apparatus commonly takes the form of a system of relays, transformers, and contactors enclosed within one or more sheet metal cabinets. For smaller motor ratings, current interruption can be accomplished by compact contactors which can be handled manually for servicing and replacement. However, for larger high-voltage motors much larger, heavier equipment is needed. Contactors for making and breaking high voltage, high-current circuits become unwieldy, and moreover require large arc chutes and greater insulation than do lower-voltage apparatus. In addition, owing to the hazards inherent in high voltage equipment the contactor apparatus which operates at such voltages is normally enclosed in a cubicle which is physically separated from other cubicle housing lower-voltage control mechanisms.
In order to maintain and repair the high-voltage contactor it is typically mounted in a carriage assembly which may be withdrawn from its cubicle for repair or maintenance, and later installed, or "racked," back into the cubicle for operation.
When the carriage is racked into a cubicle, in order to make electrical contact with the large, heavy current-carrying members a considerable amount of force must be applied to the carriage. At the same time, very little distortion or flexure can be tolerated. For this reason and because of the considerable weight of the large, heavy contactor assemblies, transformers and associated elements which are borne by the carriage, contactor carriages have traditionally been of large, massive design. Popular constructions of such carriages have commonly included one-piece castings. While such castings are rigid and strong, they require considerable machining for the mounting of different elements on them and moreover they are expensive and heavy. Recently, efforts have been made to fabricate carriages from individual structural elements. Such approaches ordinarily include clamping the various structural elements together in a jig or fixture, and welding or otherwise assembling basic structural elements together in order to form a rigid, metal carriage assembly which may carry contactors, insulating barriers and other necessary elements. It will therefore be appreciated that it would be highly desirable to provide a contactor carriage assembly which is rigid and strong, while being lower in weight and formed from lighter fabricated components than those heretofore known.
It is therefore an object of the present invention to provide an improved construction for a contactor carriage assembly.
Another object is to provide a contactor carriage assembly of integrated construction which incorporates component supports into an overall, rigid structure.
Yet another abject is to provide a contactor carriage design which may be assembled together with bolts, while accurately maintaining all critical dimensions.